Carbon brush for dynamo-electric machines



May 27 1924.

- w. w. JARVIS CARBON BRUSH FOR DYNAMO ELECTRIC MACHINES Filed Feb. 21. 1921 Patented May 27, 1924.

UNITED STATES PATENT OFFICE.

WILLIAM WALTER JARVIS, 01? BATTERSEA, LONDON, ENGLAND, ASSIGNOR TO THE MORGAN CRUGIBLE COMPANY LIMITED, 0]? BATTER-SEA, LONDON, ENGLAND CARBON BRUSH FOR- DYNAMCT-EL'ECTRIG MACHINES.

Application filed February 21, 1921.

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Be it known that I, VILLIAM ALTER Janvrs, a subject of the Kingot Great Brit ain, residing at Battersea \Vorks, Battersea, London, England, have invented new and useful Improvements in or Connected with Carbon Brushes for Dynamo-Electric Machines, of which the following is a specification. I

This invention relates to carbon brushes for use in connection with dynamo electric generators or electric motors.

In such machines it is usual, in order to facilitate the passage of the current between the carbon brush and the holder in which it is mounted, to provide a flexible copper conductor or pigtail attached at one end to the brush and at the other end to the holder. In certain cases, particularly when the machines are small, the pigtail is'liable to touch live metal of opposite polarity, or metal which is normally earthed, and in order to prevent this it is necessary to insulate the pigtail. Various well-known methods have been adopted for this purpose, as, for instance, the insulation of the pigtail by means of beads or cotton sleeving, or tape wrapped spirally round the pigtail, but all these methods possess disadvantages, chief amongst which may be mentioned the fact that they adversely affect the flexibility of the pigtail and impair its facility for the dissipation of the heat generated therein by the passage of the current. The object of this invention is to provide an improved method of insulation by which the defects of the existing methods are ob via'ted.

To this end, according to the invention, I make use or" an insulation comprising a flexible openwork tube of a bore slightly larger than the diameter of the pigtail over which it loosely fits. V For example, the tube may be composed of a strip of material, such as vulcanized fibre, leatheroid or the like, which is spirally wound into a flexible tube the bore of which is slightly larger than the diameter of the pigtail over which it is passed and loosely fits. The tube may be advantageously made by softening the said strip and winding it into a spiral on a mandrel. Any suitable pitch for the spiral may be selected, the object being to make the pitchsmall enough to prevent contact between the pigtail and Serial No. 446,728.

live or earthed metal, but otherwise as large as possible to facilitate the dissipation of heatfrom the conductor, by the provision of spaces as wide as is practically possible between the adjacent turns of the strip. As the insulation tube is itself flexible and fits loosely on the pigtail, the flexibility of the latter is completely retained.

Or, two or more fibre or like strips may be plaited into a tube to fit loosely around the pigtail in the manner above described and so as to leave spaces or interstices for the dissipation of heat.

To enable the invention to be fully understood, I will describe it by reference to the accompanying drawing, in which Fig. L illustrates a perspective view of a carbon brush provided with a copper conductor or pigtail insulated in accordance with the invention, and Fig. 2 is an enlarged detail view of the device, showing the insulation spaced apart from the pigtail.

a indicates the carbon brush and b the flexible copper conductor or pigtail. One end of this pigtail is attached to the brush a in any convenient way, but preferably by the connection known as the Battersea connection and described in the specification of British Patent No. 16175 of 1907 granted to the Morgan Crucible Company Limited and another. The other end of the said pigtail is furnished with the ordinary terminal c by means of which itcan be attached to the brush holder.

(Z indicates the strip of material, such as vulcanized fibre, leatheroid or the like. The strip is first spirally wound to a tubular t'orm, of bore somewhat greater than the diameter of the pigtail, this being advantageously effected by first softenin the said strip and then winding it spiraly on a mandrel. The tube so formed is then passed on to the pigtail Z) and since it is flexible and fits loosely on the pigtail the flexibility of the latter is nowise impaired.

As above described, the pitch of the spiral is made sufiiciently small to prevent contact between the pigtail b and live or earthed metal, but is as large as possible, without preventing the attainment of this result, for the purpose of facilitating the dissipation of heat from the pigtail b.

Although in the drawing the flexible insulating tube is shown made from a single strip (Z spirally coiled, yet, it will be understood that the said tube may be 'formed from two or more strips plaited together, in such a manner as to provide spaces or interstices between the adjacent portions of the strip for the purpose specified. 7

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed I declare that what I claim is 1. A carbon brush provided with a flexi ble pigtail, having a flexible openwork tubular insulation of a bore somewhat larger 2A device as claimed in claim 1, said tubular insulation being composed of a suitable material such as vulcanized fibre spirally wound so as to provide spaces between the adjacent coils for the dissipation of heat from the pigtail. A

WILLIAM WALTER JARVIS. 

